Modern communications and data networks are comprised of nodes that transport data through the network. The nodes may include routers, switches, bridges, or combinations thereof that transport the individual data packets or frames through the network. Some networks may offer data services that forward data frames from one node to another node across the network without using pre-configured routes on intermediate nodes. Other networks may forward the data frames from one node to another node across the network along pre-configured or pre-established paths. Some networks implement a routing or switching network constructed using network virtualization and clustering technology, such as a United Router Farm (URF).
A URF comprises a set of routers or switches that are clustered together using network virtualization technology. The URF is an autonomous system in which a master router is in charge of the routing control functionality for other routers (or switches) in the cluster, so that the remaining routers may implement simpler logic and have lower cost. In a URF, a plurality of access nodes may be each connected to one or more aggregation nodes. The aggregation nodes may be configured as the master nodes and the access nodes may serve as the slave nodes. The master nodes perform routing functionalities, and calculate and distribute forwarding tables to the slave nodes. The slave nodes may serve as remote line cards for the master nodes that have a simplified forwarding engine, since their routing functionality is offloaded to the master nodes. A URF comprising hundreds or thousands of nodes can be viewed as a single logical router, which simplifies packet forwarding, management, and provisioning processes in the network. The logical router (or URF) can also improve network scalability by providing node plug-and-play with zero or minimal configuration, which may reduce capital expenditure (capex) and operating expenditure (opex).
The URF scheme separates the control plane and the data plane where the slave node behaves as a remote line card of the master node. The forwarding engine on the slave is controlled at the master node via a routing protocol stack. This is different from traditional routers in which the control plane and the data plane are collocated (at the same node or box) and may communicate over a Peripheral Component Interconnect (PCI) bus in the same box. Thus, existing mechanisms and protocols for traditional routers are not suitable for the URF architecture to control packet forwarding reliably and efficiently in the network.
One approach introduced to control packet forwarding in a URF is using a virtual local area network (VLAN) with a proprietary protocol from Cisco™ for packet forwarding. The VLAN approach may comprise using VLAN tags in the packets to forward the packets in the URF. However, this approach requires direct connectivity between master and slave nodes, and thus does not work for some topologies, such as a ring topology. Another restriction is that the VLAN does not allow more than about 4,000 VLAN tags in a network, which limits network scalability. This VLAN approach restricts the application for use in networks with a hub and spoke topology but not the ring topology. Thus, this VLAN scheme is not used in widely deployed ring topology based networks.